Integrated circuit chip manufacturers fabricate semiconductor devices by various combinations of processes. Plasma processes that provide high etch selectivity, good anisotropy, good uniformity, low ion-induced damage, low particulate contamination, and meet fabrication throughput requirements are mandatory for the etching of submicrometer features. These objectives often impose conflicting and stringent requirements. Typically, selectivity is improved and ion-induced damage decreases while anisotropy and uniformity worsen as the operating process pressure increases. The persistent drive towards higher device integration density presents stringent requirements on the anisotropy of etch profiles and on the precise control of the widths of etched lines and spaces. This is to be achieved while maintaining the necessary selectivity and etch rate specifications.
One example of a process technology that is expected to achieve the above requirements is radio-frequency or RF-assisted remote microwave plasma etching. It is well recognized that this etch technology allows for fast etch rates, high selectivity, and low damage. However, it is also recognized that this technique suffers from unacceptable etch profiles, particularly at room temperature, as evidenced by the observed isotropic etching of the sidewalls. Isotropic sidewall etching (undercut) should be eliminated to improve the anisotropy of the etch profile.
One technique in eliminating the isotropic sidewall etch is to chill the semiconductor substrate down to cryogenic temperatures. Temperatures required for acceptable anisotropic etch profiles usually occur below -100.degree. C. Conventional liquid-coolant-based refrigeration equipment cannot achieve such low temperatures or provide sufficient cooling load capacities. Further, conventional refrigeration systems utilize bulky heat exchangers and noisy compressors that are unsuitable for semiconductor device processing. Such systems occupy large and expensive clean room floor space, cause vibrations, and generate undesirable particulates in the semiconductor processing chamber. The thermal response time of conventional systems is slow and unsuitable in applications where rapid temperature cycling or adjustments to cooling load changes have to be implemented.
From the foregoing, it may be appreciated, that a need has arisen for a method and apparatus for chilling semiconductor substrates that provide low temperature, good thermal response time, improved cooling load capacity, and are suitable for semiconductor device processing. A need has also arisen to provide a method and apparatus for chilling semiconductor substrate that improves etch profile anisotropy by eliminating isotropic sidewall etch. Further, a need has arisen for a method and apparatus for chilling semiconductor substrates at a reduced cost and without bulky equipment as compared to conventional refrigeration systems.